The design of auxiliary fuel system for civil aircraft involves several systems on aircraft which is related to complicated installing environment and the coupling of inputs and outputs for multiple systems. As the design of refueling system, it needs to consider the coupling of refueling flow and venting flow. Based on the software FloMASTER, a validation method is proposed in this paper which takes the refueling and venting system of auxiliary fuel system as the study objects. The main research content is based on the simulation including the change of gas pressure in fuel tank under different refueling pressure, the requirement of the venting flow and the pressure capacity of fuel tanks, which will be evaluated whether it meets the design specifications or not. The results show that:1) the capacity of venting tubes in fuel tanks meets the requirement of venting flow while the auxiliary fuel system is refueled on the ground; 2) the gas pressure in auxiliary fuel tank will not over the maximum design pressure value of auxiliary fuel tank during ground refueling; 3) the pressure in both auxiliary fuel tank and original fuel tank will meet the design pressure under limiting condition(the failure of ground refueling cutting-off).